A role of immune-mediated reaction in the pathogenesis of primary and secondary herpes simplex uveitis was studied in rabbits. The results of the study indicated that primary herpes simplex uveitis is dually mediated; first by the infection of the uveal tissue by live herpes simplex virus, later by the immune-mediated mechanisms. Secondary uveitis is mainly induced by the immune mechanisms. The chemotactic factor appeared to play an important role in the pathogenesis of primary and secondary uveitis since the chemotactic activity of the aqueous humor of these eyes paralleled the cytology of the cellular infiltrates in the aqueous. Daily topical application of dexamethasone significantly suppressed clinical manifestations of secondary herpes simplex uveitis. However, the treatment appeared to enhance the virus growth in the uveal tissues.